I. Technical Field
The present invention relates to sealing devices for rotary fluid machines that are preferably applied to rotary fluid machines such as multistage compressors and relates to rotary fluid machines.
II. Description of the Related Art
It is known that, in rotary fluid machines such as multistage centrifugal compressors, the occurrence of swirling stall causes vibration of a rotary shaft (shaft vibration), and the point of occurrence of the shaft vibration is the compressor operating limit.
A known method of preventing swirling stall is a method involving reducing the area of a flow passage of a vaneless portion, in other words, a method of reducing the height of the flow passage in the rotational axis direction. In this way, the flow velocity components outward in the radial direction speed up in the vaneless portion to prevent the flow separation at an impeller outlet port, thereby suppressing the occurrence of swirling stall.
However, when the area of the flow passage of the vaneless portion is reduced, there is a problem in that the loss occurring in the vaneless portion increases, reducing the efficiency of the compressor.
On the other hand, in multistage centrifugal compressors, an interstage labyrinth is disposed to prevent fluid leakage between stages (see Japanese Examined Utility Model Application, Publication No. SHO-58-022444 and Publication of Japanese Patent No. 2756118, for example).
It is also known that a flow of fluid leaking from a rear stage to a front stage via the interstage labyrinth functions to suppress the above-mentioned swirling stall. Specifically, the above-mentioned leakage flow forms a circulation flow that flows through the rear stage, the interstage labyrinth, and the diffuser of the front stage in this order, and the circulation flow increases the velocity of radially-outward flow components of a fluid flow flowing in the diffuser. Therefore, flow separation at the impeller outlet port is prevented, and the occurrence of swirling stall is suppressed.
In the method of preventing swirling stall by the interstage labyrinth described in Japanese Examined Utility Model Application, Publication No. SHO-58-022444 and Publication of Japanese Patent No. 2756118, however, there is a problem in that the compressor efficiency is reduced.
Specifically, in order to prevent swirling stall, radially-outward flow components of the fluid flow flowing in the diffuser need to have a certain velocity or more. To obtain this flow velocity, a clearance of the interstage labyrinth needs to be increased. When the clearance is thus increased, swirling stall can be prevented, but the flow rate of a fluid flow leaking from the rear stage to the front stage is increased, leading to a problem in that the compressor efficiency is reduced.
Further, the leakage flow passing through the clearance of the interstage labyrinth does not include flow velocity components in the circumferential direction of the rotary shaft, and, when the leakage flow flows behind the impeller, flow velocity components in the circumferential direction are imparted to the leakage flow by the rotation of the impeller. In other words, the impeller performs extra work for imparting flow velocity components in the circumferential direction to the leakage flow, thereby causing a problem in that the compressor efficiency is reduced.
Furthermore, there is a problem in that, when a fluid flow flowing into the diffuser from the impeller outlet port and a fluid flow flowing into the diffuser from behind the impeller are joined, loss occurs because of the difference in flow velocity of circumferential flow velocity components, thereby reducing the compressor efficiency.
The present invention has been made to solve the above-described problems, and an object thereof is to provide a sealing device for a rotary fluid machine and a rotary fluid machine capable of reducing a decrease in efficiency and suppressing swirling stall in a multistage rotary fluid machine.
In order to achieve the above-described object, the present invention provides the following solutions.
According to a first aspect, the present invention provides a sealing device for a rotary fluid machine, including: a housing that rotatably accommodates a rotary shaft having a plurality of impellers; a plurality of guide parts that are mounted on an inner surface of the housing, between the plurality of impellers, that extend along at least one of a radial direction and an axial direction of the rotary shaft, and that impart flow velocity components in the rotation direction of the rotary shaft to fluid passing through therebetween; a partition part that connects other ends of the plurality of guide parts opposite to ends thereof mounted on the housing and that serves as a partition between spaces between the plurality of guide parts and an outside space; a first seal part that is an annular protrusion extending in the radial direction, that forms a first gap with respect to the rotary shaft or the housing, and that blocks fluid flowing toward the plurality of guide parts; and a second seal part that is an annular protrusion, that forms a second gap with respect to the rotary shaft or the partition part, and that blocks fluid flowing through the outside space.
According to the first aspect of the present invention, since a route is formed in which fluid circulates from the rear-stage-side impeller to the front-stage-side impeller via the first gap and the spaces between the plurality of guide parts or the second gap, the occurrence of swirling stall in the rotary fluid machine can be prevented.
Further, most of the fluid flowing from the rear-stage-side impeller toward the plurality of guide parts through the first gap flows through spaces between the plurality of guide parts, which spaces are defined by the plurality of guide parts, the housing, and the partition part, and the rest of the fluid flows through the second gap. Since the plurality of guide parts impart flow velocity components in the rotation direction of the rotary shaft to the fluid passing through therebetween, it is possible to prevent a decrease in efficiency in the rotary fluid machine.
In the first aspect of the invention, it is preferable to have a structure in which the other ends of the plurality of guide parts face the impeller extending from the rotary shaft outward in the radial direction; and the partition part extends in the radial direction, is formed in a ring-plate-like shape to connect the other ends, and makes the fluid pass inward in the radial direction through the spaces between the plurality of guide parts.
By doing so, when fluid flowing through the spaces between the plurality of guide parts is directed inward along the radial direction, the length of the sealing device along the axial direction can be reduced. Further, it is possible to reduce the axial length of the multistage rotary fluid machine in which the sealing device of the invention is provided.
Further, it is possible to increase the lengths of the guide parts in the direction along the flow of fluid, that is, the lengths thereof in the radial direction, without changing the length of the sealing device along the axial direction. Therefore, the flow velocity components in the radial direction can be imparted more reliably to the fluid while the fluid flows between the plurality of guide parts.
In the first aspect of the invention, it is preferable that the other ends of the plurality of guide parts face an outer circumferential surface of the rotary shaft; and the partition part extend in the axial direction, be formed in a cylindrical shape to connect the other ends, and make the fluid pass along the axial direction through the spaces between the plurality of guide parts.
By doing so, the fluid flowing through the spaces between the plurality of guide parts is directed from the first seal part toward the plurality of guide parts along the axial direction, thereby making it possible to reduce the length of the sealing device along the radial direction.
In the above-described structure, it is preferable that the second seal part be an annular protrusion extending in the radial direction; and a step part that radially expands the outer circumferential surface of the rotary shaft be provided at a location of the rotary shaft facing the first seal part or the second seal part.
By doing so, the step part, which radially expands the outer circumferential surface of the rotary shaft, is provided at a location facing the first seal part or the second seal part, thereby making it possible to change the relative position of the first gap and the second gap in the radial direction. Therefore, fluid that has passed through the first gap is prevented from directly flowing into the second gap, and the sealing performance of the sealing device can be improved.
In the first aspect of the invention, it is preferable that the guide parts be plate-like members inclining in the rotation direction of the rotary shaft outward in the radial direction, or be plate-like members inclining in the rotation direction of the rotary shaft from the first seal part toward the second seal part.
By doing so, the guide parts are formed in a plate-like shape, which is simpler than the shape of blade-like guide parts, for example, and therefore the sealing device is easily manufactured.
In the first aspect of the invention, it is preferable that the guide parts be blade-like members extending along the radial direction or the axial direction and be curved in the rotation direction of the rotary shaft outward in the radial direction, or be curved in the rotation direction of the rotary shaft from the first seal part toward the second seal part.
By doing so, the guide parts are formed in a blade-like shape and are curved in the rotation direction of the rotary shaft, thereby making it possible to effectively impart flow velocity components in the rotation direction of the rotary shaft to the fluid passing through the plurality of guide parts, compared with a case where the guide parts are formed in a plate-like shape.
According to a second aspect, the present invention provides a rotary fluid machine including the sealing device according to the first aspect of the present invention.
According to the second aspect of the present invention, since the sealing device according to the first aspect of the present invention is provided, it is possible to allow fluid to flow from the rear-stage-side impeller toward the front-stage-side impeller via the sealing device and to prevent the occurrence of swirling stall in the rotary fluid machine.
It is possible to impart flow velocity components in the rotation direction of the rotary shaft to fluid flowing through the sealing device from the rear-stage-side impeller toward the front-stage-side impeller and to prevent a decrease in efficiency in the rotary fluid machine.
According to the sealing device for a rotary fluid machine of the first aspect of the present invention and the rotary fluid machine of the second aspect thereof, since a route is formed in which fluid circulates from the rear-stage-side impeller to the front-stage-side impeller via the first gap and the spaces between the plurality of guide parts or the second gap, an advantage is afforded in that the occurrence of swirling stall in the rotary fluid machine can be prevented.
Further, since the plurality of guide parts impart flow velocity components in the rotation direction of the rotary shaft to fluid passing through therebetween, an advantage is afforded in that it is possible to prevent a decrease in efficiency in the rotary fluid machine.